1. Technical Field
The present invention relates to a method for producing a thermoplastic elastomer composition.
2. Background Art
Olefin-based thermoplastic elastomer compositions have molding processability comparable with that of olefin-based thermoplastic resins and therefore are being used in a broad range of applications, for instance in automotive parts, household electric appliance parts, medical device parts, electric wires, and so on. Such olefin-based thermoplastic elastomer compositions can be obtained by subjecting an olefin-based rubber and a polyolefin-based resin to dynamic thermal treatment in the presence of a crosslinking agent.
As the crosslinking agent, organic peroxides, sulfur, alkylphenol resins, and so on have been used. In some cases, a crosslinking aid is used with the crosslinking agent; compounds having two or more polymerizable double bonds, such as N,N-m-phenylenebismaleimide and trimethylolpropane trimethacrylate, metal halides, such as stannous chloride and ferric chloride, metal oxides, such as zinc oxide and magnesium oxide, and so on have been used as such a crosslinking aid.
As a method for producing such an olefin-based thermoplastic elastomer composition, for example, JP 2-235949 A has disclosed a method in which a component composed of a polypropylene-based resin, an ethylene-propylene-ethylidene norbornene copolymer rubber, a paraffinic oil, and stannous chloride and an alkylphenol resin is fed into a Banbury mixer, and then the polypropylene-based resin, the ethylene-propylene-ethylidene norbornene copolymer rubber, and the paraffinic oil are subjected to dynamic thermal treatment in the presence of the alkylphenol resin, which is a crosslinking agent, and the stannous chloride, which is a crosslinking accelerator, in the Banbury mixer.
However, in the case where an alkylphenol resin has been used as a crosslinking agent, an extruded sheet of the resulting thermoplastic elastomer may have poor appearance.